Hormones can act to cause a tissue to accumulate a specific set of proteins during development. Ovarian maturation in the fruit fly Drosophila melanogaster is under hormonal control and involves the disposition of vitellogenic proteins into yolk particles. It is the goal of this project to understand in molecular terms the ways in which specific hormones elicit the synthesis of yolk proteins. The approach to the problem is threefold: 1. The Endocrine tissues involved in vitellogenesis and the hormones they produce must by elucidated. 2. The Molecular Biology of the interaction of the hormone with the target cells and the response of the cell must be studied. And 3. The Genetics of the yolk proteins and regulatory elements controlling their expression must be described. Our experiments using the classical techniques of the endocrinologist have suggested the hypothesis that ecdysterone causes the synthesis or secretion of vitellogenin (Vg) from the fat body, while the juvenile hormone causes the ovary to sequester Vg from the blood. Messenger RNA has been isolated from fly abdomens, and it directs the synthesis of Vg in an in vitro translation system. Female sterile mutants unable to undergo normal vitellogenesis have been discovered, some of which have faulty endocrine functions, and others abnormal ability to sequester Vg. In the next few years we hope to be able to understand the interactions of hormones with the genetic machinery in controlling gene activity.